In an optical transmission apparatus which is provided with a great number of laser diode, photo-detector or semiconductor optical amplifier array modules and transmits or receives optical signals via optical fiber arrays, disposal of excess pigtails of optical modules mounted on a board is important. Especially, in the transmission apparatus for processing the high bit rate optical signals of several Gb/s, it is necessary to control the lengths of the optical fibers in the order of cm. Two ways can be devised for controlling the lengths of the optical fibers. In the first way, the lengths of the respective pigtails are separately controlled internally in the optical module. In the second way, an optical fiber connector supporting the external optical fibers, the lengths of which are respectively controlled, is fabricated, and the optical module is connected with and removed from the aforementioned optical fiber connector. In the second way, the lengths of the optical fibers can be more easily controlled than in the first way, and the space on the board can be saved.
On the optical module to be connected with the optical fiber connector designed for a multi-mode optical fiber array in which tolerance limits of misalignments of optical axes of the optical fibers are comparatively loose, many developments of optical parallel interconnection modules have been reported. However, with the further expansion of the transmission capacity and the extension of the transmission distance expected in future, the realization of the optical module to be connected with the single mode optical fibers is expected.
Moreover, in order to realize miniaturization of the optical module having the function of an optical switching and a wavelength selecting in the multi-channel optical transmission system, a hybrid integrated structure in which an optical device is integrated with an optical waveguide device, such as a planar optical circuit, is desired. In the aforementioned structure, it becomes necessary to connect the optical waveguides with the single mode optical fiber array with high effeciency.
Hitherto, as means for connecting the optical waveguides with the optical fiber array which lies between the optical waveguides and the optical fiber connector, the structure shown in FIGS. 1A and 1B is known (M. Takaya, et. al., Technical Digest Integrated Photonics Research, IWH2, 1996)
As shown in FIG. 1A, an optical module 110 is fabricated by sticking a plug component 111 and an optical waveguide chip 112 together. In the optical waveguide chip 112, plural optical waveguides 113 are formed in parallel each other. On the inner surfaces of the plug component 111 and the optical waveguide chip 112, V grooves 111a and 112a are respectively formed, and a positioning of the plug component 111 relative to the optical waveguide chip 112 is performed by inserting pins 114 into the V grooves 111a and 112a.
Near both the side ends of the plug component 111, guide holes 115 for positioning the plug component 111 relative to the optical fiber connector 120 shown in FIG. 1B are formed. As shown in FIG. 1B, plural optical fibers 121 running in parallel with each other are buried in the optical fiber connector 120, and guide holes 122 for positioning the optical fiber connector 120 relative to the optical module 110 are formed near both the side ends of the optical fiber connector 120.
Positioning of the optical fiber connector 120 relative to the optical module 110 are performed by inserting guide pins (not shown) into the guide holes 122 and 115, and thereby the optical waveguides 113 of the optical module 110 are connected with the optical fibers 121 of the optical fiber connector 120.
In the structure for connecting the optical fibers 121 with the optical module 110 by means of the optical fiber connector 120, it is very important that end faces of the optical fibers 121 and the optical guide 113 are flattened. Accordingly, both the end faces are specularly polished.
However, in the aforementioned conventional optical module, it is necessary to stick the waveguide chip and the plug component together with high accuracy in order to specularly polish the end face of the optical waveguide, but the aforementioned sticking process is very difficult. The reason is that, although positionings of the optical waveguides in the horizontal and vertical directions are successfully performed because of the existence of the pins, the aforementioned structure has no means for positionings the optical waveguides in the direction of the optical axes thereof.
Moreover, a heavy load is applied to the optical module in case that the optical fiber connector is connected with or removed from the optical module. However, since the optical module is formed by sticking the optical waveguide chip and the plug component together with adhesion, the optical module cannot withstand the aforementioned load applied thereto.
As a method for increasing the strength of the optical module, a following one can be devised. That is to say, the optical waveguides are sandwiched by two parallel reinforcing plates near the end face of the optical waveguides, which are opposed to the fiber block (the optical fiber array) face to face. Then, the position of the fiber block relative to the optical waveguides is optimized by monitoring intensities of lights emitted from the fiber block, and the are stuck together. However, according to this method, since complicated works for aligning to the optical axes are added, it is undesirable from viewpoints of an increasing in cost and low productivity.